This application relates generally to communications networks, and more particularly, to testing communication lines.
Recently, there has been an increased demand for plain old telephone systems (POTS's) to carry high-speed digital signals. The demand has been stimulated by home access to both the Internet and distant office computers. Both types of access typically employ a POTS line as part of the path for carrying digital signals.
POTS's lines were built to carry voice signals at audible frequencies and can also carry digital signals as tones in the near audible frequency range. Modem digital services such as ISDN and ADSL transmit data at frequencies well above the audible range. At these higher frequencies, POTS's lines that transmit voice signals might transmit digital signals poorly. Nevertheless, many telephone operating companies (TELCO's) would like to offer ISDN and/or ADSL data services to their subscribers.
Telephone lines between a TELCO switch and a subscriber's premises are frequent sources of poor performance at the high frequencies characteristic of ISDN and ADSL transmissions. Nevertheless, high cost has made widespread replacement of these subscriber lines an undesirable solution for providing subscribers with lines capable of supporting ISDN and ADSL. A less expensive alternative would be to use only those subscriber lines that are acceptable for transmitting high-speed digital data or to replace those that are not.
To enable limited replacement of inadequate lines, TELCO's have placed some emphasis on developing methods for predicting which subscriber lines will support data services, such as ISDN and ADSL. Some emphasis has been also placed on predicting frequency ranges at which such data services will be supported. Some methods have also been developed for finding faults in subscriber lines already supporting data services so that such faults can be repaired.
Current methods for predicting the ability of subscriber lines to support high-speed digital transmissions are typically not automated and labor intensive. Often, these methods entail using skilled interpretations of high frequency measurements of line parameters to determine data transmission abilities. At a network scale, such tests are very expensive to implement.
The problem of qualifying lines for data services has been described in several patents. U.S. Pat. No. 6,385,297 by Faulkner, et al. which is hereby incorporated by reference.
Use of neural networks for finding faults on a telephone line was described in PCT Application WO98/4428 “System and Method for Telecommunications System Fault Diagnosis”. However, that patent does not recognize the value of using a neural net to qualify a line for high-speed data services nor does it describe an appropriate neural net topology for that purpose.
Using a neural network for line qualification is more directly described in Line Qualification with Neural Networks, 09/409,141 published as PCT application WO 00/25206, which is hereby incorporated by reference. However, it would be desirable to improve upon that technique to obtain more accurate results, such as by decreasing the number of lines that are incorrectly classified as unable to support high speed data services without unacceptably increasing the number of lines that are incorrectly classified as capable of supporting high speed data services. It would also be desirable to accurately predict the speed at which a particular line under test can operate.